Simulating Diurnal Variability Over the Southeast United States

This study analyzes diurnal variations in precipitation and temperature over the Southeast United States as produced by the dynamical downscaling, high-resolution Regional Spectral Model (RSM). The model is forced over the period 1989-1999 using three reanalysis packages: The National Center for Environmental Predictions - Department of Energy Reanalysis 2 (NCEP-DOE-R2), the European Centre for Medium-Range Weather Forecasts' 40 Year Reanalysis (ERA-40), and the 20th Century Reanalysis (20CR). Furthermore, model runs are done using both the Relaxed Arakawa-Schubert (RAS) and Kain-Fritsch 2 (KF2) convective schemes. It is found that the RSM best simulates the phase and amplitude of observed rainfall and temperature when forced with NCEP-DOE-R2 using the KF2 convective scheme. The amplitude of diurnal variations in precipitation and temperature are then analyzed from the perspective of surface vegetation characteristics and latitude. Vegetation types are categorized according to the 12 NOAH vegetation indices used in the NOAH Land Surface Model. Finally, the driving relationships between diurnal amplitudes in precipitation and temperature, total land surface heat flux, 10-meter wind speed and cloud cover are explored.